The frame assembly of large multi-cell field erected cooling towers is a complex, labor-intensive, repetitive and potentially dangerous process. While sizes and relative dimensions vary widely, large scale field erected cooling towers often consist of as many as eight or more units or “cells,” and a typical cell can be 40 or more feet in height, 60 or more feet in length, and 60 or more feet in width. Each cell is typically composed of 4 to 10 component sections or “bays,” which can be longitudinal or transverse. FIG. 1 shows (on the bottom) a nearly finished cooling tower having eight cells, totaling nearly 500 feet in length. At the top of FIG. 1, an unfinished cooling tower of equivalent size is shown in the frame assembly stage.
Frame assembly is generally carried out in one of two ways. According to a first “stick” assembly process, each individual piece of the frame is moved into place, one at a time, either by hand, or with assistance with a crane or lift, and sequentially bolted or otherwise fixed to adjacent pieces. As the frame rises into the air, workers climb up, down, and through already assembled portions of the frame to place and bolt new pieces. Hence, beginning from bottom to top, and from one side to the other, the frame is assembled manually, one piece at a time. For safety, workers use safety harnesses attached to already-assembled portions of the frame, and the harnesses need to be detached and moved to a different part of the frame and the assembly progresses.
According to a different assembly process, sequential two dimensional sections of the frame are assembled on the ground, then lifted into place with a crane or other lift, one at a time, and fixed to adjacent sections with transverse members. While this process reduces the time workers spend in the height of the structure placing and connecting the elements that contribute to the height of the structure, the workers must still move in and among the structure at various heights connecting each two dimensional section or “face” to the next.